Recent data continue to indicate that use of the insecticide DDT may have adverse effects on human health, but essentially no findings on this topic have been replicated, so the question is still open. Whether DDT has adverse effects is important because DDT is still used for malaria control in about 12 countries, and current recommendations by the World Health Organization that support DDT use are based on the assumption that it has basically no adverse health consequences for humans. DDE is the major metabolite of DDT. Experiments in animals indicate that DDE blocks androgen action and that exposure before birth can have adverse effects on male reproduction. In addition, two previous human studies suggest that higher exposure to DDE is associated with a shortended duration of lactation. Breast feeding prevents infant death. Therefore, DDT use may have the effect of increasing infant death. Furthermore, recent data suggest that DDT/DDE may cause pregnancy loss in humans. Additional information about these potential adverse effect are needed. Mexico used the insecticide DDT for malaria control until 1999;many people there in tropical areas have elevated blood levels of the DDT metabolite, DDE. My project in Mexico has two phases;both are based on the same group of subjects. I conducted phase 1 of this study to examine the relation between maternal serum levels of DDE in relation to evidence of decreased androgen action in 781 newborn males in Tapachula, Mexico. All phase 1 subjects were enrolled in 2002-2003;the response rate was 95%. Phase 2 of this study began in FY 2004. This study followed 757 women and children enrolled in Phase 1, to determine if DDT exposure is related to reduced length of lactation among mothers. In addition, the offspring were followed to examine early-life DDT exposure in relation to infection and growth. Follow-up has been completed. Last years progress: For phase 2, a paper on the reliability of reporting length of lactation was published. The mothers'reports of the duration of lactation in this population were highly reliable. A report on the relation of DDE with growth was submitted for publication;next we will examine childhood infections as an outcome.